Small computing devices, commonly referred to as “handheld devices” or portable computing devices, have become more common as the processing power of the devices has increased (referred to as a “handheld device”). Such devices are increasingly being used in the medical field. For example, a handheld medical device could be given to a patient in a hospital, and the patient may use the device to record when the patient experiences pain or to control the dispensing of pain medication. A typical handheld device generally functions using an operating system that supports various functions and includes functionality allowing a user to load additional programs (or modify existing programs) into the devices. One problem with conventional handheld devices is that the execution of one program may cause interference with, or affect, the execution of another program on the device. Moreover, with the capability of downloading or modifying programs, a user or other unauthorized person may be able to load new programs, modify existing programs, or interfere with the operation of the handheld device, either intentionally or inadvertently, thus interfering with the operation of the handheld device. Such interference may be inconvenient during normal use but may cause serious problems when the device is used in a medical environment.